Cushion is the underlayment for carpet to help the carpet resist matting and crushing. Cushion is sometimes called padding or pad or lining. Cushion also provides added acoustical, comfort and insulation benefits as well as longer wear life for the carpet. Carpets installed over cushion or with attached cushion typically last much longer and are easier to maintain than carpet directly glued to the hard surface.
NOTES: For pad under berber carpet, the general rule is the bigger the loop in the berber, the firmer the padding should be. If radiant heat is used, the cushion used must be a low insulating type, such as a relatively thin, flat cellular sponge rubber or synthetic fiber cushion.
There are three basic types of cushion, which are foam, rubber and fiber. Each type is further subdivided into two or three varieties.
- Foam comes in three varieties:
Prime urethane foam is a firmer version of the same cushioning used in upholstered furniture, mattresses and automobile seats. Two liquid ingredients are combined to form a large mass of foam, which is then sliced into sheets for use as carpet cushion. There are three types of prime urethane carpet cushion: conventional prime, grafted prime and densified prime cushion. Prime urethane foam grades are measured by density, or weight of the material per cubic foot.
Bonded urethane foam (sometimes called rebond) is formed by combining chopped and shredded pieces of foam into one solid piece. It frequently has a surface net for ease of installation and improved performance. Bonded foam grades are also measured by density. Rebond pad can cause yellowing of olefin carpet and stain-resist nylon carpet. Rebond pad sometimes contains BHT (Butylated Hydroxytoluene). BHT is a common preservative used in many plastics and even in bread. BHT was removed from most olefin backings in 1985 because of yellowing of carpet fibers. Many cushion manufacturers have now also removed BHT from their products.
Mechanically frothed urethane foam is made with carpet backing machinery. Frothed urethane cushions are made from a process originally developed to apply cushioned backings to carpet. The urethane foam cushioning is applied to a sheet of nonwoven material, forming a carpet cushion product with a typically higher density and firmer feel.
- Sponge Rubber: There are two specific types of sponge rubber carpet cushion. Grades for both are measured by weight in ounces per square yard.
Waffled sponge rubber is made by molding natural or synthetic rubber to a rippled or waffled surface. This variety produces a soft, resilient cushion whose luxurious feel is particularly useful for residences. Waffle rubber pad is often used improperly. The waffle part of the padding gives it a thickness that is mostly air, and as a result, any of this type of padding rated less than 90 ounces is still too soft for today’s carpets. Frequently, the rubber used to make this type of pad is held together with clay binders that break down with use.
Flat sponge rubber is a firm, dense cushion, which has a flat surface and is normally used in large-scale commercial applications and with loop type (or berber) carpet.
- Fiber: There are two basic types of fiber carpet cushion: natural fiber and synthetic carpet fiber or felt. A third type, recycled textile fiber, is occasionally seen. The grade of fiber cushion is determined by its weight in ounces per square yard. Fiber cushions tend to have a firm “walk” or “feel.”
Natural fibers include felt, horsehair and jute. These are, of course, highly susceptible to rotting if over-wetted, odor development and natural degradation. Some natural fiber cushions have been treated with a water-soluble dye that can stain a wet carpet. Fiber pads are used sometimes to limit the movement in an area rug. The key is density. Felt cushion density is by weight of ounces per square yard.
Synthetic fibers / synthetic felt include nylon, polyester, polypropylene and acrylics, which are needle-punched into relatively dense cushions which have a firm feel and, as with other types of cushion, can be made in virtually any weight, to stand up under light, medium, or heavy traffic, which is how they are usually classified.
The quality of a carpet cushion is determined by density (the weight of one cubic foot of the cushion), not thickness and softness. If the cushion is too soft and thick, the carpet excessively flexes with traffic, the backing is put under enormous strain and the carpet will delaminate. Foam pads should not lose more than half their height when you pinch them. Cushion under most residential carpet should be a thickness no greater than 7/16 inch.
With urethane foam cushion, density is rated at pounds per cubic foot. For example, a 5-pound rebond pad would weigh 5 pounds per cubic foot. The Carpet and Rug Institute recommends a residential pad of at least 5 pounds and 3/8 inch thickness for light traffic (a living room), and a pad of 6.5 pounds and 3/8 inch for heavy traffic (hallways). These are minimum guidelines. Residential cushion should not be any thicker than 7/16 inch. Berber carpet requires a firm cushion and is usually sold as “berber cushion.” For commercial installations, the minimum should be 12-14 pounds with a thickness of 1/4 - 3/8 inch.
Attached cushion is cushion material permanently bonded to the back of carpet and rugs by the manufacturer to provide additional dimensional stability, thickness and padding. Materials used include polyurethane, sponge rubber, PVC, high-density foam and latex.
Woven carpet must be installed over an extra heavy super dense fiber pad or, in some cases, a heavy flat frothed foam.